Hi Klaus, Maybe "base number" or something like that? Yes, that's exactly what I'm trying to find out. We've used a self-made lookup function until now, but in the course of the switch from SER to OpenSER I try to eliminate as much self-written stuff as possible for easier maintenance. I'm aware of the performance impact, but I'm currently just playing around with some stuff to see what's possible and maybe usable... We use a related approach in the e164.info tree. I'm quite curious about the performance of the different possibilities, so I find it rather interesting to compare these things in a test-bed... Andy